A technique for determining the type of a cell and performing charging operation according to the type of the cell is known. For instance, JP Publication No. 2002-10508 describes detection of a connection of an external cell through use of a mechanical mechanism and electrical detection performed by way of a terminal for use in detecting a connection, wherein a resistance value or an impedance value of a cell is read beforehand and the type of an external cell connected to equipment is determined by means of taking the value as an ID signal. Further, the patent publication also describes exchange of an electrical pulse signal between a detection section and a cell pack by use of a microprocessor, or the like, to thus determine the type of a cell connected to the equipment.
JP Publication No. 2001-54243 describes computation of the amount of change between the voltage of a cell terminal acquired when a voltage is applied to the cell terminal from the outside and the voltage of the cell terminal acquired when no voltage is applied to the cell terminal from the outside, thereby determining, from the amount of voltage change, whether the cell is a primary cell or a secondary cell.
However, if the type of a cell can be determined simpler without use of the mechanical mechanism, such a determination is desirable. When the type of a cell is determined by use of a terminal voltage, the capability of determining an overdischarge of the secondary cell as well as the capability of distinguishing between a primary cell and a secondary cell are preferable. Specifically, in addition to the case where the terminal voltage of the secondary cell is substantially zero and where the secondary cell is not present, there is a conceivable case where the secondary cell is present but simply remains overdischarged. In reality, if the secondary cell is determined not to be present despite the secondary cell remaining overdischarged, there may arise a case where originally-required recharging of the secondary cell is not performed. Further, when the primary cell and the secondary cell are of the same type but differ from each other in terms of the position of a terminal, the primary cell and the secondary cell are housed in a single housing. Therefore, detection of a difference between the positions of the terminals in principle enables distinction between the primary cell and the secondary cell. However, when the difference between the positions of the terminals cannot be detected for reasons of physical damage, and a like case, it may be the case where the battery cells cannot be distinguished from each other.